Internal combustion engines have a power stroke defined by combustion and expansion of working gases. In motor vehicles, it is required in many geographic regions to treat the discharged working gases for reducing emissions, particularly HC, CO and NOx and particulate emissions.
Present emission reducing technology requires that the discharged working gases need to be at a certain minimum temperature in order for the catalytic after-treatment process to be effective. If conventional engines were adjusted, i.e. by varying compression ratios, fuel ratios and valve timing to run most efficiently, the discharged exhaust gases would be cooler than the required minimum temperature. Therefore, current engine designs face a tradeoff between optimizing the work extraction from the working gases and leaving enough energy in the form of heat to allow catalytic converters to effectively clean the discharged working gases.
Thus, present internal combustion engine designs, for example Diesel, Otto, Rotary, or Atkinson cycle engines when used in an automotive vehicle compromise between maximum practical expansion during the power stroke and leaving enough heat in the output gases to provide for effective catalytic after-treatment. Typically, once the hot exhaust gases are treated, they are run through a muffler, or merely discharged to the atmosphere.
What is needed is an engine design that can capture more energy from the hot exhaust gases and convert it to work output, thus increasing the efficiency of an internal combustion engine but still provide for effective emission reduction.